DAC1006/1007/1008 — Simple Hookup for a “Quick Look”
(Continued)
7.4 Digitally Controlled Amplifier/Attenuator
An unusual application of the DAC,
Figure 21, applies the in-
put voltage via the on-chip feedback resistor. The lower op
amp automatically adjusts the V
REF IN
voltage such that
I
OUT1
is equal to the input current (V
IN
/Rf
B
). The magnitude
of this V
REF IN
voltage depends on the digital word which is
in the DAC register. I
OUT2
then depends upon both the mag-
nitude of V
IN
and the digital word. The second op amp con-
verts I
OUT2
to a voltage, V
OUT
, which is given by:
Note that N=0 (or a digital code of all zeros) is not allowed or
this will cause the output amplifier to saturate at either
±
V
MAX
, depending on the sign of V
IN
.
To provide a digitally controlled divider, the output op amp
can be eliminated. Ground the I
OUT2
pin of the DAC and
V
OUT
is now taken from the lower op amp (which also drives
the V
REF
input of the DAC). The expression for V
OUT
is now
given by
DS005688-56
FIGURE 21. Digitally Controlled Amplifier/Attenuator
DS005688-27
FIGURE 22. Digital to Synchro Converter
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PrintDate=1998/11/17 PrintTime=11:38:10 46711 ds005688 Rev. No. 4
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Extract
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